A flyback converter power supply is a buck-boost converter with the inductor split to form a transformer, so that the voltage ratios are multiplied with an additional advantage of galvanic isolation.
Many power supplies are of the “constant voltage” type. That is, they attempt to maintain constant output voltage across a rated current range, from zero to some maximum current. Within normal load ranges, voltage regulation employs a feedback signal related to output voltage. There are two common ways to generate this feedback signal. The first is to use a secondary reference and amplifier with an optocoupler to transfer the signal to the regulation controller. The second method utilizes a separate, “auxiliary” winding on the transformer and senses error signals from the auxiliary winding. The auxiliary winding may also supply operating power to the controller itself. The latter feedback method, referred to as “primary-side regulation,” can provide good output voltage and current regulation without requiring the ancillary secondary feedback components described above.